The 12 months of work experience specific to the accountability of scrum master or product owner can be met at any time once you've attended an A-CSM® or A-CSPO® course. Please note that the work experience must be within the past five years of the current date.
Please ensure your work experience is entered on your Scrum Alliance® account for it to be validated. Once you've reached at least 12 months of counted work experience, you'll receive a notification email from Scrum Alliance will be able to claim your advanced certification on your account dashboard.
To learn how to enter work experience on your account, please see this article: How do I add work experience for my advanced or CSP® level certification?